Radiation-sensitive emulsions, elements, and processes for making same



States atent @filice 3,033,682 Patented May 8, 1962 3,033,682 RADIATION-SENSITIVE EMULSIONS, ELEMENTS, AND PROCESSES FOR MAKING SAME Heman Dowd Hunt, Eatontown, N.J., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del.,

a corporation of Delaware No Drawing. Filed Nov. 12, 1959, Ser. No. 852,190 14 Claims. (Cl. 96-108) This invention relates to radiation-sensitive colloidsilver halide emulsions, emulsion layers, and elements embodying the same, and to processes for making the same. More particularly, it relates to such products which are light-developable, have high speeds and resolving power and have good contrast and image stability.

Radiation-sensitive papers adapted for light recording, e.g., oscillographic recording, are known. These papers are of the developing-out and print-out type. The developing-out type, as the name implies, requires that the exposed material be chemically developed, fixed and washed in order to provide a stable visible image on said material. The print-out type of material requires no development step and may or may not be fixed. The printout type are generally much slower than the developingout type and the images are unstable and have a short life.

A third type of radiation-sensitive material especially suitable for light-writing and oscillographic recording comprises a colloid silver halide layer which, when exposedto a high intensity source of light, forms a latent image which can then be developed by exposure to diffuse daylight or artificial light of lower intensity. Such direct writing emulsions are faster than print-out emulsions and require no chemical development.

Proposed emulsions of the third type include silver bromide emulsions which have incorporated therein sulfur-containing compounds as halogen acceptors, e.g., thiourea and thiosemicarbazides. The background and image densities obtained from such emulsions, however, are not sufliciently stable to permit rapid access to or prolonged examination of the recorded images. It has been proposed to make such radiation-sensitive emul sions by introducing silver thiocyanate into a silver bromide emulsion. The sensitivity of this emulsion while greater than pure silver bromide emulsions containing halogen acceptors can be further increased by the use of halogen acceptors. However, such emulsions, after being light-developed by daylight or incandescent light, do not provide a stable image. Upon prolonged exposure to ordinary illumination, the background darkens, thus reducing the ratio between background and image densities. Also, where the exposing light contains a high proportion of ultraviolet light, subsequent exposure, after lightdevelopment, causes an increase in background density and rapid regression of the light-developed image. It is necessary to treat the light-developed image in a liquid developing bath containing a silver halide solvent to intensify and preserve the contrast or ratio of background to image density of the originally light-developed image. Treatment in a fixing bath is also recommended.

The chemical sensitization of photographic developingout emulsions and print-out emulsions with stannous salts is known. Silver halide emulsions containing very small quantities of lead salts are also known. However, these compounds have been used in developing-out emulsions in extremely small quantities.

The light-developable, direct-writing, light-sensitive elements, e.g., films and papers, of this invention comprise a support and a layer of a water-permeable organic colloid having dispersed therethrough light-sensitive silver halide grains of large grain size which preferably are in the range of from 0.1 to microns in diameter and containing 0.5 to 120 or more, and preferably 5 to 60 mole percent, of a stannous salt, 0.1 to 20 or more, and preferably 0.5 to 5 mole percent, of a plumbous salt and an excess of bromide ions, all per mole of silver.

The novel silver halide emulsions can be made by precipitating the silver halide or mixture of silver halide in an aqueous solution containing a water-permeable organic colloid in any conventional manner. Thus, they can be made by slowly adding an aqueous solution containing a water-soluble silver salt, e.g., silver nitrate, to an aqueous solution containing (1) a water-soluble halide or a mixture of such halides, e.g., lithium, sodium, potassium, calcium, magnesium or ammonium chloride, bromide or iodide and (2) a water-permeable organic colloid of high molecular weight and possessing protective colloid properties, preferably gelatin. In making silver bromide emulsions, it is preferable to use either calcium bromide or magnesium bromide in an amount sufficient to provide a considerable excess of bromide ion over that necessary to react with the silver salt, e.g., silver nitrate.

Suitable stannous salts include stannous chloride, stannous bromide and stannous sulfate.

Suitable lead or plumbous salts which can be used include lead nitrate and lead acetate.

After precipitation and ripening to provide the proper grain size, a relatively large percentage, e.g., 0.5 to 120 or more mole percent of stannous salt and 0.1 to 20 or more mole percent of plurnbous salt, per mol of silver, are added. The emulsion may or may not be digested, as desired, and additional gelatin or other water-permeable colloid is added to bulk up the emulsion. The resulting aqueous emulsion can then be coated without further treatment. If desired, the emulsion may be washed but, in this case, additional water-soluble bromide must be added to maintain an excess of bromide ions of about 50% to or more.

When washed emulsions of the pure silver bromide type are used, other soluble bromide salts in addition to the calcium and magnesium salts mentioned above may be used with equivalent results provided that bromide ions are present in considerable excess, e.g., about 50% or more in excess when the flowable or molten emulsion is coat-ed onto the surface of the support. For example, potassium, sodium and/or ammonium bromide may be used as an additive after Washing. In the case of washed emulsions, the tin and lead salts usually are added as a final addition before coating or just before making the final gelatin addition.

The preferred method of exposing and processing material coated with the emulsions of the invention comprises exposing the material to radiation from a xenon tube or high-pressure mercury-arc lamp containing a high proportion of blue and ultraviolet radiation for a period ranging from about 0.1 to 10,000 microseconds or more. After exposure, the material may be light developed by exposure to daylight or low intensity incandescent or fluorescent light or by the use of photofiood lamps commonly used in photography.

When using fluorescent lights of the type used in ordinary ofiice lighting, the image is easily visible in approximately 0.1 to 15 seconds with development to maximum image density in several minutes. With this type of development, a much more stable background and more permanent image is obtained. Light-development by means of photoflood lamps can result in a readable image in about one second or less, with only a slight increase in background density. Although the ratio of image density to background density is somewhat lower under this latter condition of light-development, a high ratio can be maintained by photographic fixing.

Speed in oscillography is measured in inches per second and is called writing speed. The source in a typical instrument designed for direct-writing papers is the Osram super high pressure mercury arc lamp Type HBO 107/1. Writing speeds are determined from the frequency of the signal and the peak to peak amplitude of oscillation as recorded on the paper.

The writing-speed determination of a material was augmented by a /2 step wedge exposure to an electronic flash sensitometer similar to that described by Wyckoff & Edgerton, Journal of the Society of Motion Picture and Television Engineers, 66, 474 (1957). This instrument uses a xenon discharge tube as the source of radiation and has available two exposure times of and 1,000 microseconds. Relative sensitivities of materials measured with this instrument may be expressed as the number of steps recorded in the image.

The recorded latent image was developed with radiation from fluorescent lighting or a reflector photo-flood lamp, GE. Rfl. #2A. Intensity was varied by distance of the lamp from the developing material.

The invention will be further illustrated by, but is not intended to be limited to, the following detailed examples.

Example I A gelatino-silver bromide emulsion was made by slowly adding an aqueous solution of silver nitrate to an aqueous gelatin solution of magnesium bromide to provide a large grained emulsion, the magnesium bromide being present in suffifiicient quantity to provide a 100% excess of bromide ion. The precipitation was carried out under an Eastman Kodak No. 613 amber safelight. The temperature during precipitation was held at 140 F. The mixture was then cooled and an aqueous solution of lead nitrate was added, followed by a glycerine solution of stannous chloride in amounts to give 1 mole percent lead ion and 10 mole percent tin ion based on the silver bromide. After digestion at 140 F. for 10 minutes, the emulsion was cooled to coating temperature and diluted to the desired viscosity. The resulting emulsion, after the addition of the usual hardeners and coating aids, was coated on an unsized paper support to give a dry coating weight of silver bromide of 40 mg. per square decimeter. The coated emulsion was dried in a conventional manner.

The coated material recorded an image at a writing speed of 20,000 inches/ second using a 2,000 cycle/ second signal and an amplitude of 3.2 inches.

Light development times and densities were determined from the step-wedge exposures using various sources as the intensifying radiation. The image color is blue-gray on a light yellow background. The results are tabulated below.

Exposure time 10 microseconds 1,000 microseconds Intensifying source Fluor- Photo- Fluor- Photoescent fiood escent flood" Source Intensity-foot candles 70 10,000 70 10, 000 Steps visible 5 21 16 Background density 0.16 0.33 0.18 0. 32

A maximum density of 0.52 was obtained when using fluorescent light development and a maximum density of 0.64 was obtained when photoflood light development was used.

Example II Example III Example I was repeated except that calcium bromide was used in place of magnesium bromide. The sensi- 4 tometric properties of the resulting coated material were similar to those of Example 1.

Example IV A silver bromide precipitation in gelatin was carried out as described in Example 1. After precipitation and ripening to obtain the desired grain size, the emulsion was coagulation washed in the manner described in Example I of Moede, US. 2,772,165. After the emulsion was redispersed, it was divided into four portions and treated as follows. To one (1) portion there was added 1 mole percent of lead nitrate and 10 mole percent of stannous chloride. To a second (2) portion there was added 1 mole percent of lead nitrate, 10 mole percent stannous chloride and mole percent of magnesium bromide. To a third (3) portion there was added 1 mole percent of lead nitrate, 10 mole percent of stannous chloride and 100 mole percent of ammonium bromide. To the fourth (4) portion there was added 1 mole percent of lead nitrate, 10 mole percent of stannous chloride and 100 mole percent of potassium bromide. These emulsions were coated on white paper and the coated emulsions were tested in a manner similar to that described in Example I. Coatings of portions (2), (3) and (4) had sensitometric properties comparable with those of the unwashed examples of Example I. The coating portion (1) had much lower density and lower image and background stability.

Example V A gelatino-silver chlorobromide emulsion was made by slowly adding an aqueous solution of silver nitrate to an aqueous gelatin solution of magnesium chloride and hydrochloric acid, the magnesium chloride being present in sufiicient quantity to provide a 100 mole percent excess of chloride ion. To this mixture was added an amount of magnesium bromide equal to 1.6 times the amount of magnesium chloride, followed by a second addition of aqueous silver nitrate in an amount equal to the first silver addition. Additional gelatin was then dissolved in the mixture and the mixture was chilled, noodled and washed to remove soluble salts. The washed emulsion was melted and an aqueous solution of magnesium bromide was added to provide a 100 mole percent excess of bromide ion. This was followed by the addition of aqueous plumbous nitrate to give 1 mole percent lead ion and stannous chloride dissolved in Cellosolve 1 to give 40 mole percent of stannous ion, all per mole of silver. A 15% by weight aqueous gelatin solution was added and the emulsion was digested at 140 F. for 10 minutes. After digestion, the emulsion was cooled to the coating temperature and a hardener, e.g., chrome alum, and water were added, and the pH was adjusted with potassium bicarbonate to 4.0. The emulsion was coated on a paper support to give a dry silver halide coating weight equivalent to 40 mg./drn. of silver bromide. The coated emulsion was dried in a conventional manner. The sensitometric properties of the resulting coated material were similar to those of Example I except that maximum image density was somewhat increased and the image density was more stable.

Example VI Example V was repeated except that mole percent stannous ion was added in place of 40 mole percent. The sensitometric properties were similar to those of Example I except that maximum image density was somewhat lower and image density stability was further improved.

Example VII A silver halide emulsion was prepared by slowly adding aqueous silver nitrate to an aqueous gelatin solution containing magnesium chloride and about 5 mole percent, per mole of silver, of hydrochloric acid. The

Monoethylether of ethylene glycol used. The silver chloride mixture was then ripened by the addition of 160 mole percent, per mole of silver, of"

magnesium bromide and the mixture was held at 140 F. for 40 minutes. Additional gelatin was then dissolved in the mixture to facilitate setting up and washing the mixture. After washing, 60 mole percent, per mole of silver, of potassium bromide was added. To the resulting emulsion there was added at 140 F. 1 mole percent of plumbous nitrate per mole of silver. After holding for 5 minutes at 140 F., the molten stannous chloride was added in the amount of 20 mole percent per mole of silver. After an additional 5-minute holding period at 140 F., 15% by weight aqueous gelatin solution was added to give a total gelatin weight equivalent to three times the weight of silver bromide present. Dextran equivalent to one-third the weight of gelatin was added to facilitate drying. The pH was adjusted to about 4.5 with potassium bicarbonate. Chrome alum was added as a hardening agent. The emulsion was then coated on a paper support to a coating weight of approximately 30 mg/dm. of silver bromide. The resulting material gave a writing speed in excess of 20,000 inches per second. The other sensitometric properties were similar to those of Example I.

Example VIII To an emulsion similar to that described in Example VII there was added an aqueous plumbous nitrate solution sufficient to give 20 mole percent of plumbous ion per mole of silver bromide. The emulsion was then coated on a paper support to give a coating weight of 30 mg./dm. of silver bromide. The writing speed was approximately 75% of that of Example VII.

Example IX To an emulsion similar to that described in Example VII there was added molten stannous chloride in sufficient amount to give a final stannous ion concentration of approximately 120 mole percent per mole of silver bromide present. The pH decreased due to stannous ions and was not adjusted. The material was coated on a paper support. The speed was not changed by the large amount of stannous ion, and the background and image densities were more stable than that with the coating having less stannous ion.

The novel radiation-sensitive, water-permeable colloid silver halide emulsions of the present invention, including those of the foregoing examples, can be modified prior to coating by the addition of optical sensitizing dyes.

Stannous chloride may be added to the emulsion from aqueous solutions but the tendency for the solution to become cloudy due to the formation of precipitataes of basic oxides on standing, especially in dilute concentrations, makes such as solution less desirable as compared to glycerine or sorbitol in which stannous chloride is very soluble; nevertheless, the cloudy aqueous solution does give good results. The use of glycerine as a solvent has the advantage that it is an anticurl agent which is especially advantageous in coatings on paper.

The sensitization of the emulsions of this invention by stannous salts is not affected by the presence of excess bromide ions and in this respect the range of concentration of bromide ion is not critical. This is of considerable advantage compared with the prior art emulsions sensitized with sulfur sensitizers as the latter emulsions are adversely affected by large amounts of excess bromide ions.

Where it is desired, other halides or combination of halides may be used to form the silver halide grains. For example, pure silver chloride, chlorobromide or iodobromide may be used. Where soluble chloride salts are used it is desirable, because of solubility product differences, to form the silver halide grains of desired composition and size and then add sufiicient soluble bromide 6 salts to provide the desired concentration of excess bromide ions. The operative association of lead salts with excess bromide ions is advantageous in that the washing step necessary in conventional emulsion making is eliminated.

In place of the gelatin binding agent used in the foregoing examples there can be substituted other natural or synthetic water-permeable organic colloid binding agents. Such agents include water-soluble or permeable polyvinyl alcohol and its derivatives, e.g., partially hydrolyzed polyvinyl acetates, polyvinyl ethers, and acetals containing a large number of extralinear CH CHOH- groups; hydrolyzed interpolyrners of vinyl acetate and unsaturated addition polymerizable compounds, for example maleic anhydride, acryl and methacrylic acid ethyl esters, and styrene. Suitable colloids of the last mentioned type are disclosed in US. Patents 2,276,322, 2,276,323 and 2,397,866. The useful polyvinyl acetals include polyvinyl acetaldehyde acetal, polyvinyl butyraldehyde acetal and polyvinyl sodium o-sulfobenzaldehyde acetal. Other useful colloid binding agents include the polyvinyl lactams of Bolton US. Patent 2,495,918; polypyrrolidone; the hydrophilic, copolymers of N-acrylamido alkyl betaines described in Shacklett US. Patent 2,833,650 and hydrophilic cellulose ethers and esters.

Suitable supports for the novel photographic emulsions of this invention include those used in the prior art for light-writing and oscillographic recording. The preferred supports are unsized flexible paper but may be of any material suitable for coating photographic emulsions containing a large proportion of soluble salts.

The novel combination of stannous and lead salts with photographic silver halide emulsions containing an excess of bromide ions produces light-developable, directwriting, light-sensitive emulsion layers of enhanced speed, resolving power and capable of more rapid light development than emulsions containing only a tin salt or free from excess bromide ions. The lead salts seem to have a supersensitizing effect on the tin salts and a lower background density is obtained. The combination of the lead salt with the tin salt makes the emulsion layer more rapidly developable. The lead salt seems to suppress the sensitivity in the unexposed areas of the emulsion layer. The light-exposed areas are more rapidly light developable. Also, the salts do not have a coagulating effect when added to the silver halide emulsions.

The photographic elements of this invention are useful for electrocardiograms, seismographic recorders, for photocopying of various images, for X-ray recording as well as for oscillography.

An advantage of this invention is that the elements have high photographic speed, permit of rapid access and have strongly contrasted stable images. These images can be read without fixing over relatively long periods, e.g., 15 to 60 minutes or more. After fixing, of course, the images are permanent.

The novel photographic elements are extremely convenient to use because they do not require wet processing. The dry processing allows the operator to see or to use a print image rapidly after recording. Still further advantages will be apparent from the foregoing description of the invention.

This application is a continuation-in-part of my copending application Ser. No. 814,954 filed May 22, 1959.

I claim:

1. A light-developable, direct-writing, light-sensitive, water-permeable, colloid-silver halide emulsion containing (1) 0.5 to mole percent of a stannous salt and 0.1 to 25 mole percent of a plumbous salt per mole of silver, and (2) at least one water-soluble halide taken from the group consisting of lithium, sodium, potassium, calcium, magnesium and ammonium chloride, bromide and iodide in an amount sufficient to provide an excess of halide ions over that necessary initially to precipitate all of the silver as silver halide.

2. An emulsion as defined in claim 1 wherein stannous chloride and plumbous nitrate, respectively, are used as said salts, and magnesium bromide is present in an amount suificient to provide an excess of bromide ions over that necessary initially to precipitate all of the silver as silver bromide.

3. An emulsion as defined in claim 1 wherein stannous chloride and plumbous nitrate, respectively, are used as said salts and calcium bromide is present in an amount sufficient to provide an excess of bromide ions over that necessary initially to precipitate all of the silver as silver bromide.

4. An emulsion as defined in claim 1 wherein said water-soluble salt is present in an amount suflicient to provide a 50% excess of halide ions over that necessary initially to precipitate all of the silver as silver halide.

5. An emulsion as defined in claim 1 wherein said colloid is gelatin.

6. A photographic element comprising a support hearing a layer of a light-developable direct-writing, lightsensitive, water-permeable colloid-silver halide emulsion containing (1) silver halide grains having average grain sizes from 0.1 to microns in diameter, (2) 0.5 to 120 mole percent of a stannous salt and 0.1 to 25 mole percent of a plumbous salt per mole of silver, and (3) at least one water-soluble halide taken from the group consisting of lithium, sodium, potassium, calcium, magnesium and ammonium chloride, bromide and iodide in an amount sufficient to provide an excess of halide ions over that necessary initially to precipitate all of the silver as silver halide.

7. An element as defined in claim 6 wherein stannous chloride and plumbous nitrate, respectively, are used as said salts and magnesium bromide is present in an amount sufiicient to provide an excess of bromide ions over that necessary initially to precipitate all of the silver as silver halide.

8. An element as defined in claim 6 wherein stannous E chloride and plumbous nitrate, respectively, are used as said salts and calcium bromide is present in an amount suflicient to provide an excess of bromide ions over that necessary initially to precipitate all of the silver as silver halide.

9. An element as defined in claim 6 wherein said water-soluble salt is present in an amount sufficient to provide a excess of halide ions over that necessary initially to precipitate all of the silver as silver halide.

10. An element as defined in claim 6 wherein said colloid is gelatin.

11. The process which comprises admixing with (a) an aqueous light-sensitive, water-permeable, colloid-silver halide emulsion containing at least one water-soluble halide taken from the group consisting of lithium, sodium, potassium, calcium, magnesium and ammonium chloride, bromide, and iodide in an amount sufficient to provide an excess of halide ions over that necessary initially to precipitate all of the silver as silver halide, (b) 0.5 to mole percent of a stannous salt, and (c) 0.1 to 25 mole percent of a plumbous salt, per mole of silver.

12. A process as defined in claim 11 wherein stannous chloride and plumbous nitrate, respectively, are used as said salts.

13. A process as defined in claim 11 wherein said Water-soluble halide is magnesium bromide and is present in an amount sufficient to provide at least 50% excess bromide ions.

14. A process as defined in claim 11 wherein said water-soluble halide is calcium bromide and is present in an amount sufiicient to provide at least 50% excess bromide ions.

Carroll Nov. 15, 1949 Jones June 17, 1958 

1. A LIGHT-DEVELOPABLE, DIRECT-WRITING, LIGHT-SENSITIVE, WATER-PERMEABLE, COLLOID-SILVER HALIDE EMULSION CONTAINING (1) 0.5 TO 120 MOLE PERCENT OF A STANNOUS SALT AND 0.1 TO 25 MOLE PERCENT OF A PLUMBOUS SALT PER MOLE OF SILVER, AND (2) AT LEAST ONE WATER-SOLUBLE HALIDE TAKEN FROM THE GROUP CONSISTING OF LITHIUM, SODIUM, POTASSIUM, CALCIUM, MAGNESIUM AND AMMONIUM CHLORIDE, BROMIDE AND IODIDE IN AN AMOUNT SUFFICIENT TO PROVIDE AN EXCESS OF HALIDE IONS OVER THAT NECESSARY INITIALLY TO PRECIPITATE ALL OF THE SILVER AS SILVER HALIDE. 